1. Technical Field
This invention relates to electrical impact wrenches, and more particularly to an electrical, variable speed impact wrench having an operator settable maximum speed control for enabling the operator to controllably limit the maximum speed, and thus the maximum torque, of the wrench.
2. Discussion
Impact wrenches are used in a wide variety of applications to quickly secure various forms of fasteners such as threaded screws and the like to a work surface. Such impact wrenches typically include an operator-engageable trigger which is electrically coupled to a speed control circuit disposed within a housing of the impact wrench. The speed control circuit is in turn electrically coupled to a motor of the impact wrench and provides a variable voltage drive signal to the motor in accordance with the degree of engagement of the trigger by the operator. In this manner the speed of the motor, and thus the torque which is applied by the motor to drive a threaded screw or other like fastener, can be controlled by the operator simply by varying the degree of engagement of the trigger.
While prior designs of impact wrenches such as that described above have proven to be successful and valuable tools for rapidly driving various forms of fasteners, one limitation has been the ease with which the operator can inadvertently engage the trigger to an excessive degree to cause the impact wrench to drive a fastener too quickly into engagement with the work surface. In such instances the unnecessarily high speed motor of the wrench causes an unnecessarily high torque to be applied to the fastener which sometimes results in breakage of the fastener as the fastener is driven into fully seated engagement with the work surface. Experienced operators of such impact wrenches may be able to exercise a degree of manual control over the trigger of the impact wrench so as to avoid or limit such breakage due to driving the fastener at too high a speed, but infrequent users frequently have difficulty consistently controlling the maximum speed of the wrench, via the trigger, so as to avoid excessive breakage of fasteners.